1. Field of the Invention
This invention relates to the synthesis and isomerization of cis- and trans-vinylic thiophosphorus acid esters and to their use.
Firstly, this invention relates to the stereospecific synthesis of cis- and trans-vinylic thiophosphate, thiophosphonate and thiophosphinate esters by reacting the corresponding vinylic alkali metal or Grignard compound with the corresponding phosphoryl disulfide or phosphoryl sulfenyl chloride.
Secondly, this invention relates to the isomerization of the above cis- and trans-vinylic phosphorus acid esters to the thermodynamically more stable mixture of geometrical isomers by free radical type chemical catalysis, e.g. via the reversible addition of thiyl radicals or by ionic catalysis, e.g. with strong protic acids.
Thirdly, this invention relates to the use of vinylic thiophosphorus esters, having a certain, i.e. cis- and transtype, geometric structure. As the main use of such esters, their pesticidal application is described.
2. Prior Art
Vinylic esters of dialkyl phosphoric acid represent an important class of commercial pesticides. (For reference, see pages 40 to 67 of a monograph, entitled "Die Entwicklung neuer insektizider Phosphorsaeure-Ester" by Gerhard Schrader which was published by Verlag Chemie in Weinheim, W. Germany, 1963.)
The biological activity of insecticidal phosphate esters in general is attributed to their inhibition of the cholinesterase enzyme (see pages 6 to 10 of the above referred Schrader monograph). The outstanding pesticidal effectiveness and safety of these esters initiated further research to find even more effective compositions and better methods for their preparation.
Several methods were described in the prior art for the synthesis of vinylic esters of dialkyl dithiophosphoric acids. The method most closely related to the present invention reacted a dialkoxy thiophosphoryl disulfide with a vinylic Grignard or lithium compound, e.g. [for reference, see article by B. Miller in J. Am. Chem. Soc., Vol. 82, page 6205, year 1960]: [(C.sub.2 H.sub.5 O).sub.2 P(S)S].sub.2 + BrMgCH = CH.sub.2 .fwdarw. (C.sub.2 H.sub.5 O).sub.2 P(S)SCH .dbd. CH.sub.2. The stereochemistry of the reaction was not examined. Apparently, it was assumed that the reaction cannot be used for the stereospecific synthesis of cis- and trans-isomers.
One of the methods for the synthesis of several commercially important vinylic phosphate pesticides, i.e. of carbohydrocarbyloxy propenyl esters of dimethyl phosphoric acids, reacts the sodium derivative of an acetoacetic ester with the corresponding phosphoryl chloride. (For reference, see pages 54 to 59 of the previous reference to Schrader.) An application of this method for the synthesis of a thiono analog is shown by the following reaction scheme: ##STR1## As indicated by the above reaction scheme, this method yields the isomer having the phosphoric and the carboxylic ester groups in cis-configuration to each other. This isomer was found to be biologically less active than the trans-isomer. A slow method of isomerizing the cis- to the trans-isomer by ultraviolet irradiation was disclosed by J. B. Stothers and E. Y. Spencer. (See Can. J. Chem., Vol. 39, page 1389, year 1961). However, no effective method was found in the prior art for the isomerization of vinylic diorgano phosphorus esters. The higher biological activity of the trans-hydrocarbyloxy propenyl esters was attributed to an additional simultaneous interaction of the strongly polar carboxylic acid ester group with a secondary site of the cholinesterase. (For reference, see A. Morello, E. Y. Spencer and A. Vardanis, Biochem. Pharmacol., Vol. 16, pages 1703 to 1710, 1967.) Difference between the activity of cis- and trans-isomers was not known or assumed for those vinylic phosphates which have no polar substituents.